Research Document - 2000/148

Spawning stock characteristics and cod recruitment success in the southern Gulf of St. Lawrence.

By D.P. Swain and G.A. Chouinard

Abstract

Recruitment rate (defined here as R, the abundance of 3 yr old cod, divided by SSB, the biomass of the spawning stock that produced them) has varied widely for cod in the southern Gulf of St. Lawrence. In particular, the rate of recruitment was remarkably high from the mid 1970s to the early 1980s. Variation in the quantity or quality of eggs produced by a unit of SSB will contribute to variation in the recruitment rate when it is estimated by R/SSB. We tested effects of spawning stock characteristics (age and size structure) on the recruitment rate of southern Gulf cod. Over the 1950-1994 period, there was no tendency for high recruitment rates to be associated with an older or more diverse age structure of the spawning stock, or with a spawning stock composed of larger fish in better condition (as measured by growth rate or weight at age). Mean age of spawners, their age diversity and the proportion of older fish in the spawning stock all declined to their lowest levels in the mid to late 1970s, when recruitment rates were at their highest. Size and growth of spawners were high both during the period of high recruitment rates in the mid to late 1970s and in the 1950s and 1960s when recruitment rates were unremarkable. Effects of indices of spawner age and size composition were not significant when included as covariates in the stock-recruitment relationship, even accounting for the effect of pelagic fish biomass on the recruitment rate. It appears that effects of characteristics of the spawning stock on recruitment success of southern Gulf cod are overshadowed by other sources of variation in recruitment rate, at least in the case of the spawning stock characteristics that we have measured

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